1. Field of the Invention
The present invention relates to an electro-optical device formed by a semiconductor element (an element using a semiconductor thin film) made over a substrate surface, and to electronic equipment (an electronic device) having this electro-optical device. Typically, the present invention relates to a liquid crystal display device or an EL display device in which a thin film transistor (hereinafter referred to as a TFT) is formed over a substrate, and to electronic equipment having that kind of display device as a display (a display section).
2. Description of the Related Art
Techniques of manufacturing a TFT on a substrate have been greatly advancing in recent years, and development of applications in active matrix type display devices is proceeding apace. In particular, a TFT using a polysilicon film has an electric field effect mobility (also called mobility) which is higher than that of a conventional TFT using an amorphous silicon film, and high speed operation is consequently possible. Therefore, it becomes possible to perform pixel control, which is conventionally carried out by a driver circuit outside of the substrate, by a driver circuit formed on the same substrate as the pixel.
This type of active matrix display device has been in the spotlight because several kinds of advantages can be obtained by making various circuits and elements on the same substrate, such as: reduced manufacturing cost, miniaturization of the display device, an increase in yield, and an increase in throughput.
However, circuits and elements having many functions are formed on the substrate of the active matrix display device. The performance of the TFTs required by the respective circuits and elements, therefore, differs when forming the circuits and elements from TFTs. For example, a TFT having high speed operation is required by driver circuits such as a shift register circuit, while a TFT with a sufficiently low off current value (the drain current value flowing when the TFT is in the off operation state) is required by switching elements in a pixel section.
In this case it becomes difficult to ensure the performance required by all of the circuits and elements by TFTs having the same structure, and this affects seriously in raising the performance of the active matrix display device.
In addition, many circuits other than the above pixel and driver circuits are necessary when using the active matrix display device as a part of electronic equipment. In particular, the formation of a memory section for temporarily recording image information on the same substrate is of great importance in expanding uses of the active matrix display device.
An object of the present invention is to provide an electro-optical device having high operation performance and reliability, in which a TFT, with a proper structure to obtain the performance required by circuits and elements formed of TFTs, is used in an active matrix type electro-optical device having a pixel section and a driver circuit section on the same substrate.
Specifically, an object of the present invention is to provide an electro-optical device having high operation performance and reliability, with proper TFT structures for a pixel section, a driver circuit section, and a memory section, respectively, formed on the same substrate.
Another object of the present invention is to improve performance and to improve picture quality of a display device by adding a memory function to an active matrix type electro-optical device. In addition, another object of the present invention is to improve the quality of electronic equipment which uses the electro-optical device of the present invention as a display.
According to a structure of the present invention, an electro-optical device comprising:
a driver circuit section having an n-channel TFT in which a portion of an LDD region, or the entire LDD region, is formed so as to overlap a gate electrode with a gate insulating film sandwiched therebetween;
a pixel section having a pixel TFT in which an LDD region is formed so as not to overlap a gate electrode with the gate insulating film sandwiched therebetween; and
a memory section having a memory transistor, is characterized in that
the driver circuit section, the pixel section and the memory section are formed on the same insulator.
According to another structure of the present invention, an electro-optical device comprising:
a driver circuit section having an n-channel TFT in which a portion of an LDD region, or the entire LDD region, is formed so as to overlap a gate electrode with a second gate insulating film sandwiched therebetween;
a pixel section having a pixel TFT in which an LDD region is formed so as not to overlap a gate electrode with the second gate insulating film sandwiched therebetween; and
a memory section having a memory transistor containing an active layer, a first gate insulating film, a floating gate electrode, a third gate insulating film, and a control gate electrode, is characterized in that
the driver circuit section, the pixel section and the memory section are formed on the same insulator.
According to another structure of the present invention, an electro-optical device comprising:
a driver circuit section having an n-channel TFT in which a portion of an LDD region, or the entire LDD region, is formed so as to overlap a gate electrode with a second gate insulating film sandwiched therebetween;
a pixel section having a pixel TFT in which an LDD region is formed so as not to overlap a gate electrode with the second gate insulating film sandwiched therebetween; and
a memory section having a memory transistor containing an active layer, a first gate insulating film, a floating gate electrode, a third gate insulating film, and a control gate electrode, is characterized in that
the driver circuit section, the pixel section and the memory section are formed on the same insulator, and in that
the third gate insulating film covers the gate electrode of the n-channel TFT and the gate electrode of the pixel TFT.
According to another structure of the present invention, an electro-optical device comprising:
a driver circuit section having an n-channel TFT in which a portion of an LDD region, or the entire LDD region, is formed so as to overlap a gate electrode with a second gate insulating film sandwiched therebetween;
a pixel section having a pixel TFT in which an LDD region is formed so as not to overlap a gate electrode with the second gate insulating film sandwiched therebetween; and
a memory section having a memory transistor containing an active layer, a first gate insulating film, a floating gate electrode, a third gate insulating film, and a control gate electrode, is characterized in that
the driver circuit section, the pixel section and the memory section are formed on the same insulator, and in that
the floating gate electrode, the gate electrode of the n-channel TFT, and the gate electrode of the pixel TFT are made from the same material, and are covered by the third gate insulating film.
According to another structure of the present invention, an electro-optical device comprising:
a driver circuit section having an n-channel TFT in which a portion of an LDD region, or the entire LDD region, is formed so as to overlap a gate electrode with a second gate insulating film sandwiched therebetween;
a pixel section having a pixel TFT in which an LDD region is formed so as not to overlap a gate electrode with the second gate insulating film sandwiched therebetween; and
a memory section having a memory transistor containing an active layer, a first gate insulating film, a floating gate electrode, a third gate insulating film, and a control gate electrode, is characterized in that
the driver circuit section, the pixel section and the memory section are formed on the same insulator, and in that
the third gate insulating film is an oxide of the material forming the floating gate electrode.
According to another structure of the present invention, an electro-optical device comprising:
a driver circuit section having an n-channel TFT in which a portion of an LDD region, or the entire LDD region, is formed so as to overlap a gate electrode with a second gate insulating film sandwiched therebetween;
a pixel section having a pixel TFT in which an LDD region is formed so as not to overlap a gate electrode with the second gate insulating film sandwiched therebetween; and
a memory section having a memory transistor containing an active layer, a first gate insulating film, a floating gate electrode, a third gate insulating film, and a control gate electrode, is characterized in that
the driver circuit section, the pixel section and the memory section are formed on the same insulator, and in that
the floating gate electrode, the gate electrode of the n-channel TFT, and the gate electrode of the pixel TFT are made from the same material, and the third gate insulating film is an oxide of the material forming the floating gate electrode.